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Exhaust Fans

01-18-2009, 01:36 PM

Hi there,

I have an old furnace blower in my shop window at the moment and want to weld a box of sorts to enclose it and run a duct from it. Has anyone else done anything like this? I could really use some ideas.

you may be able to find an old resturant hood to use a lot of going out of buisiness places going on now days.
get the stainless steel ones (more costly) or the old steel ones (cheaper) i have a 10 footer

Comment

Make a sheet metal duct that is a bit larger that the hole an the blower.
You can put a dampener in the line the control the flow.
Most blowers are squirrel cage type. It will have 2 places to draw in air.
Another option is to put the blower in the center of where ever.
Run flex duct off the intakes, hard pipe the discharge to the outside.
That way you can run the flex to where you need it.
Cool thing about a squirrel cage, you can choke them off and the amps go down. In other words, they will slip and unload the motor.

Be safe
Jeff

Give more than you get and
you will get more than ya need.
This is true for the good and bad
that life puts out.

Comment

You need some form of "make-up air" for these to work. Either an open door, window, or some other "leak".

Creating a vacuum isn't likely as there's little chance the building is that air tight to begin with. Welding in a vacuum would probably be ideal (no need for shield gas if there's no oxygen, and then you'd need a breather mask and fresh air supply), but you're not going to get that kind of environment with something as inefficient as a furnace fan even if the room was sufficiently sealed.

As I've mentioned before on this forum, I've got a 24" "whole house" fan that is marketed as an alternative to air conditioning. It has two speeds, and acts as an exhaust fan for my 24x35' shop. I have no regrets about installing that thing and find it's incredibly effective at clearing plasma smoke and dust.

Syncrowave 250DX
Invison 354MP
XR Control and 30AAirco MED20 feederThermal Dynamics Cutmaster 81Smith O/A rigAnd more machinery than you can shake a 7018 rod at

Comment

[QUOTE=Fishy Jim;173327]You need some form of "make-up air" for these to work. Either an open door, window, or some other "leak".

Creating a vacuum isn't likely as there's little chance the building is that air tight to begin with. Welding in a vacuum would probably be ideal (no need for shield gas if there's no oxygen, and then you'd need a breather mask and fresh air supply), but you're not going to get that kind of environment with something as inefficient as a furnace fan even if the room was sufficiently sealed.

As I've mentioned before on this forum, I've got a 24" "whole house" fan that is marketed as an alternative to air conditioning. It has two speeds, and acts as an exhaust fan for my 24x35' shop. I have no regrets about installing that thing and find it's incredibly effective at clearing plasma smoke and dust.[/QUOT

make up air to make what work i just left out the filters and it seems to work fine on the resturant hood

Comment

If you're plumbing your fumes outside the building (which you should if you're going to the extent of having a fan), you need somewhere to get the same volume of air to replace what's been discharged: i.e. make-up air.

If all you're doing is sucking the fumes away from where you're directly working, and it's not being sent outside, then you're just running the air through a duct and back into the same room like a portable fan would. And in that situation, all the toxic gasses being produced from the weld pool are still in the air you're breathing.

It's possible the restaurant hood has it's own vent built into it to provide flow from the back side to make up for what's being pulled through by the fan.

Syncrowave 250DX
Invison 354MP
XR Control and 30AAirco MED20 feederThermal Dynamics Cutmaster 81Smith O/A rigAnd more machinery than you can shake a 7018 rod at

Comment

it's just one of those green fan and motors that used to be in a furnace. i currently have it stuck in the window and it works o.k. but needs some duct from it. It sucks outside. I'm wondering if it needs to be totally enclosed with just the hole for the ducting or what's the best thing to build around it. I was thinking to build a sheet box but not sure if i can leave the one side open?

Comment

To make a "box" for the fan look at a furnace. Minus the heat exchanger that is what you want . A air handler. Run the discharge outside and you should be good. You could call a mechanical contractor in your area for a old furnace to make this.